Flow cytometry is a major tool for basic research in immunology, molecular and cell biology, and genetics. It has been widely used by immunologists to investigate lymphocyte development and function and by cell biologists to study calcium mobilization, cell cycle and to sort cells based on cell surface markers. With the advancement of new reporter genes such as green fluorescent protein (GFP), flow cytometry has also become a major research tool for molecular biologists in investigating gene expression and to mark and sort expressing cells. Research generated from using flow cytometers has advanced our understanding in basic biological processes, infectious diseases and cancer. The MIT CCR has operated the Flow Cytometry Core Facility since 1987. Its mission is threefold: (1) to provide CCR Investigators and their laboratories with access to cutting-edge methods in flow cytometry, in the form of both assisted and unassisted cell sorting, by maintaining state of the art instrumentation, along with the technical and intellectual expertise necessary to operate it, in one location;(2) to offer state-of-the-art training in the use and maintenance of cell sorting instrumentation to all CCR researchers;and (3) to provide a source of expertise on experimental design, reagent selection and data analysis and interpretation through interactions with facility staff. Price comparisons show that the cost of services to CCR Investigators is highly competitive with those charged by other academic or commercial flow cytometry facilities both within the Boston/Cambridge area and nationwide.